Season the sirloin steak on both sides with salt and pepper.
Heat half of the oil in a non-stick pan over medium heat. Add the steak and cook on both sides until you reach the desired temperature using a thermometer (see below). Once cooked, remove from the pan and set aside to rest.
Add the remaining oil to the pan. Sauté the garlic and onion until soft, about 3 minutes. Stir in the broth and soy sauce, then bring to a simmer. Add broccoli, cover with a lid, and simmer until tender for about 5-7 minutes.
Dissolve the cornstarch in an equal amount of water. Slowly stir the mixture into the simmering pan until the sauce thickens to a smooth consistency.
Slice the steak against the grain and serve with broccoli. Lightly spoon the sauce over top. Serve with bread.